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title: MariaDB Connector/C Compatibility: An Update on CONC-821
description: MariaDB Foundation addresses CONC-821, a regression in MariaDB Connector/C where a maintenance update changed how mysql_stmt_bind_result() handled...
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og:description: MariaDB Foundation addresses CONC-821, a regression in MariaDB Connector/C where a maintenance update changed how mysql_stmt_bind_result() handled...
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# MariaDB Connector/C Compatibility: An Update on CONC-821

**[MariaDB.org](https://daily.dev/sources/mariadb-foundation)** · 4 min read · 0 upvotes · 0 comments

## Summary

MariaDB Foundation addresses CONC-821, a regression in MariaDB Connector/C where a maintenance update changed how mysql_stmt_bind_result() handled caller-provided length values, silently resetting them and breaking applications (including Qt-based apps and the Rust ORM Diesel) that relied on the previous, undocumented behavior. The fix restores the original behavior, documents it explicitly, and adds regression tests. Sergei Golubchik confirmed the direction but a Connector/C 3.4.11 release with the complete fix has no confirmed date; the temporal-column case is already addressed while string and BLOB cases still need work. Users are advised to check their specific Connector/C package and revision, since distributions like Fedora already ship patches independently of upstream.

## Full article

daily.dev links to this article rather than hosting it. Read it at the original source: <https://mariadb.org/mariadb-connector-c-compatibility-an-update-on-conc-821>

## Questions this post answers

### Why did my MariaDB Connector/C application start treating date/time values as absent after an update?

A recent MariaDB Connector/C update changed mysql_stmt_bind_result() to reset caller-provided length values instead of preserving them, an undocumented behavior many applications relied on. As a result, a date/time value could reach the result buffer correctly while its length field showed zero, causing the application to treat it as absent. This affected Qt-based applications and the Rust ORM Diesel, and is tracked as issue CONC-821.

_daily.dev helps developers track connector regressions like CONC-821 before they hit production._

### Is there a fixed release of MariaDB Connector/C for the CONC-821 length value bug?

Not yet as a confirmed upstream release; Sergei Golubchik wants a Connector/C 3.4.11 release to include the fix but cannot promise a date, and the temporal-column case has been addressed while string and BLOB cases still need work. Distributions may already carry patches independently, for example Fedora's mariadb-connector-c 3.4.9-2.fc44 explicitly lists a CONC-821 patch.

_Developers deciding when to upgrade MariaDB Connector/C can follow fixes like this one on daily.dev._

### How do I check if my MariaDB Connector/C package is affected by the CONC-821 regression?

Check the exact Connector/C package your application uses, including its full package revision and source, not just the MariaDB Server version, since distributions can carry independent patches. Ask your application or distribution maintainer which maintained package addresses the issue, then test the operation that originally failed against that package.

_Teams debugging connector regressions like CONC-821 can keep up with fixes on daily.dev._

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---

Tags: [#testing](https://daily.dev/tags/testing), [#infrastructure](https://daily.dev/tags/infrastructure), [#backend](https://daily.dev/tags/backend)

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